Chemical mechanical polish (CMP) is a common practice in the formation of integrated circuits. Typically, CMP is used for the planarization of semiconductor wafers. CMP takes advantage of the synergetic effect of both physical and chemical forces for polishing of wafers. It is performed by applying a load force to the back of a wafer while the wafer rests on a polish pad. Both the polish pad and the wafer are counter-rotated while a slurry containing both abrasives and reactive chemicals is passed underneath. CMP is an effective way to achieve truly global planarization over the entire wafer.
CMP processes typically involve various rinse steps. Conventionally, polish pads and wafers were rinsed with de-ionized (DI) water. The advantageous feature of the DI water is that there will be no undesirable particles left on wafers or polish pads. However, the conventional rinse method using DI water also suffers from drawbacks. First, DI water cannot thoroughly remove the by-products of the CMP, thus a considerable amount of residues was found to be left on wafers after rinsing. Particularly, organic residues are hard to remove even if additional cleaning solutions are used.
Second, DI water, due to its property of lacking ions, has a low conductivity, and thus cannot release the static electricity charges generated in the polishing and the cleaning steps. This results in serious metal line galvanic corrosion by charge transfer. Particularly, significant galvanic corrosions were found in copper lines and other metal features.
Third, with a considerable amount of particles remaining on the polish pads, the lifetime of the polish pads is shortened, resulting in increased CMP cost. In addition, the lifetimes vary significantly from pad to pad, causing difficulty in the monitoring of the polish pads. Accordingly, what is needed in the art is a new rinse method capable of cleaning wafers and polish pads more thoroughly.